In nuclear-reactor power stations, high-temperature and high-pressure steam is generated in a reactor and flows to a turbine or the like through a main steam pipe. The main steam pipe is provided with a main steam isolation valve (MSIV) for isolating the flow of steam in case of an emergency. The isolation valve is attached to the main steam pipe at an angle of 45.degree..
In order to maintain the operability of the main steam isolation valve, it is periodically disassembled and inspected and adjusted. Since the space where the isolation valve is installed is narrow and in order to limit the exposure to radiation as low as possible, a device for disassembling and reassembling the main steam isolation valve has been long desired which is to be so designed and constructed that the disassembly and reassembly of the isolation valve can be accomplished within a short time period and in a simple manner.
So far many workers use chain blocks for disassembling and reassembling the isolation valve. The valve stem must be carefully withdrawn and then inserted again in such a way that the valve stem may be prevented from being bent. Therefore, as shown in FIG. 1, three chains 4a, 4b and 4c extended respectively from chain blocks 2a, 2b and 2c are securely fixed to three points of the isolation valve 1 and the chains 4a, 4b and 4c are pulled or loosened so that the valve stem can be withdrawn or inserted along the axis of the isolation valve 1. According to this method, there arise some problems. Firstly, many skilled labors are needed. Secondly, it takes a long time to adjust the isolation valve. Thirdly, labors tend to be exposed to radiation too much. Furthermore, there is a problem that the valve stem 3 is subjected to bending because the direction in which the valve stem 3 is withdrawn or inserted is not stabilized.
The present invention was therefore made to substantially overcome the above and other problems encountered in the prior art mode for disassembling and reassembling a main steam isolation valve. The primary object of the present invention is to provide a device for disassembling and reassembling a main steam isolation valve which can quickly disassemble and reassemble the main steam isolation valve with a high degree of accuracy without the need of skilled labors, which can accomplish the disassembly and reassembly of the main steam isolation valve in a safe manner and which requires only a minimum installation and working space.
The above and other objects, effects and features of the present invention will become more apparent from the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.